Abstract

The energy E_o by which one of the three Jahn-Teller potential wells becomes lower than the other two in Cu²⁺:ZnTiF₆.6H₂O single crystal at phase transition temperature, T_cl are determined at temperatures below T_cl for different Cu²⁺concentrations from the electron paramagnetic resonance (EPR) spectra. As the sample is cooled, it is found that for high Cu²⁺ concentration, E_o increases below T_cl  at a rate much slower than that for low concentration and over a much broader temperature range. With the increase of Cu²⁺ concentration, T_cl is found to decrease significantly. These findings appear to have a bearing on the monoclinic distortion that proceeds in this system below T_cl. Qualitative explanation of the decrease of T_cl with Cu²⁺ impurity concentration is presented. E_o is negligibly small for Cu²⁺ concentrations above certain limits means that the barrier height is also vanishing for such Cu²⁺ concentrations that is, phase transition of host lattice ceases. This is likely the reason for non-existence of phase transition in some compounds like CuTiF₆.6H₂O and ZnSiF₆.6H₂O belonging to the same class with ZnTiF₆.6H₂O.

Key words: ZnTiF₆.6H₂O, Cu²⁺, Jahn-Teller potential.